Title of Invention

A PROCESS FOR MAKING LOW ALLOY STEEL WITH IMPROVED WEAR RESISTANCE PROPERTIES

Abstract

A low alloy steel with improved wear resistant properties comprising chemical compositions of C = 0.12 - 0.18% by wt., Mn = 0.8 - 1.10% by wt.. Si = 0.30 -0.50% by wt., S = upto 0.020% by wt., P = upto 0.030% by wt., Cr = 0.50 - 0.90% by wt., Mo - 0.20 - 0.40% by wt., V = 0.02 - 0.06% by wt., Cu = 0.20 - 0.30% by wt., Ni = upto 0.12% by wt., Al = 0.02 - 0.08% by wt and B = 0.003 - 0.006% by wt. and a process for manufacturing the same. The low alloy steel with improved wear resistant properties is specifically useful as sinter screen in steel plant and also as wear resistant plates in ore and coal handling plants

Full Text

The present invention relates to process for manufacture of a low alloy steel with improved wear resistant properties In plant the sinter screen made of stainless steels suffers from high rate of wear due to its low hardness Since the sinter particles arc hard enough to make the indent in steel components the same result in the net loss of weight The screen is made by punching the stainless plate and set at inclined angle under continuous vibration The sinters falling on the surface slide down to the conveyor belt Thus huge amount of sinter causes degradation of steel plates which result in loss of material and time for charging I The basic object of the present invention is to provide a low alloy steel having selective chemical constitution which would have improved wear resistant properties and avoid the above discussed problems of the known art Another-object of the present invention is to provide a process for producing low alloy steel with improved wear resistant properties Yet another object is to provide a process for producing of low alloy steel plates for use as sinter screen in steel plant Yet further object is directed to provide a low alloy steel which would be useful as wear resistant plates in ore and coal handling plants Yet further object of the invention is to provide a low allow steel with high wear resistant property and a process of manufacturing the same which would be cost effective Thus according to one aspect of the present invention there is provided a low alloy steel with improved wear resistant properties comprising a selective chemical composition of C = 0 12 -0 18% by wt. Mn = 0 8 - 1 10% by wt, Si = 0 30 - 0 50% by wt, S = upto 0 020% by wt, P = upto 0 030% by wt, Cr - 0 50 - 0 90% by wt. Mo = 0 20 - 0 40% by wt, V = 0 02 - 0 06% by wt Cu = 0 20 - 0 30% by wt, Ni = upto 0 12% by wt. Al = 0 02 - 0 08% by wt and B = 0 003 - 0 006% by wt. balance being Fe 1 Preferably, the alloy of the invention comprises C=0.12-0.18% by wt, Mn=0.8-1 10% by wt., S1=0.30-0.50% by wt., S= upto 0.020% by wt., P= upto 0.03% by wt , Cr=0.50-0.90% by wt, Mo=0.20-0.40% by wt., V=0.02-0.06% by wt., Cu=0 20-0.30% by wt., N1= upto 0.12% by wt., A1=0.02-0.08% by wt., B=0.003-0.006% by wt, balance being Fe Thus, the low alloy steel of the invention has been obtained utilizing selective alloying contents Cr, Cu, V, Mo, B, etc. which achieve good wear resistant properties and would be cost effective. According to another aspect of the invention there is provided a process for manufacture of low alloy steel-with improved wear resistant properties having chemical composition of C = 0.12 - 0.18% by wt., Mn = 0.8 - 1.10% by wt., Si = 0.30 - 0.50% by wt., S = upto 0.020% by wt., P = upto 0.030% by wt., Cr = 0.50 - 0.90% by wt., Mo = 0.20 - 0.40% by wt., V = 0.02 - 0.06% by wt., Cu = 0 20 - 0.30% by wt., N1 = upto 0.12% by wt., A1 = 0.02 - 0.08% by wt. and B = 0.003 - 0.006% by wt, balence Fe comprismg providing the molten steel of desired chemical composition ; tapping the molten steel in the temperature range of 1600 - 1660°C with or without addition of further ingot/concast ; forming blooms from the molten metal ; soaking the blooms ; and obtaining the finished steel there from preferably as plates in the minimum temperature of 800°C such as to thereby produce the required low alloy steel with high wear resistant properties The invention is described hereunder in greater detail with reference to the non-limitmg exemplary embodiments illustrated in accompanying figures wherein Figure 1 is a flow diagram showing basic steps involved in the manufacture of the low alloy steel of this invention. 2 Figure 2 illustrate the mechanical properties as a function of temperatures in the laboratory testing. Figure 3 shows the bar chart of the mechanical properties as a function of thickness and heat treatment. Figure 4 illustrates the hardness variation as a function of tempering temperature in the laboratory testing. Figure 5 illustrates the effect of heat treatment on wear loss of steel in the laboratory testing. Figure 6 shows the component, called as cold sinter screen, obtained of the low alloy steel of this invention. As illustrated in figure 1 the process of the present invention comprises the following steps in sequence : (a) producing the molten steel of required chemical composition in both basic oxygen furnace (BOF) and electric arc furnace (EAF) using iron ore, spar, burnt dolo, sand, mill scale steel strips and ferro alloys as raw materials ; b) tapping the molten steel is tapped at 1630±30°C in a preheated ladle with addition of a part of the ferro alloys in ladle ; ?? c) top pouring of the molten steel to form ingot; d) the ingots are rolled after soaking at 1300±20°C for 3-5 hrs. or alternatively molten steel is concast directly into blooms at the tundish temperature of 1540- 1550°C-with high bending point temperature (>800°C). e) soaking of the blooms at about 1250°C for period of 1 min per mm thickness of the blooms and finished rolled in between 900-950°C into plates. f) The plates are next air cooled to ambient temperature. The mechanical properties of the steel produced following the above process of the invention are next determined in laboratory. First the steel is austenitised in temperature range of AC3 and AC3 + 50°C for the period of 1 min per mm thickness followed by oil quenching and then tempering. The variation of strength as a function of temperature noted is shown in figure 2,. Similarly the strength shown in figure 3 reveals the effect of thickness and heat treatment. The tempering is conducted to ascertain the optimum hardness as shown in figure 4 upto 700°C. Upto 250 - 300°C the hardness does not change much but only stresses are relieved. Above 300°C there is loss in hardness drastically. This is used to increase the hardness which is basic requirement for improving the we. resistant properties. The mechanical properties of the alloy steel of the invention achieved one represente in following table I. TABLE - I MECHANICAL PROPERTIES OF STEEL STEEL condition YS (kg/mm2) UTS (kg/mm2) % EI Room Temp. 77.35 86.63 13.80 200°C 68.77 96.28 9.80 300°C 65.20 101.47 12.00 400°C 74.41 96.57 10.73 The wear properties are determined as ASTM standard. The wear loss as a function of heat treatment is shown in figure 5. The. plates are subjected to the fabrication by using gas cutting and punching the required sizes of slots. This is austenitised in the range of AC3 and AC3 + 50°C at the rate of 1 min per mm thickness of plates followed by oil quenching and ther tempering is carried out at 250 ± 15°C at the rate of 1 min per mm thickness. Thus the hardness of the plates are increased upto 380 BHN as compared to stainles steel plates which has a hardness of 140 BHN. 4 The plate obtained following the present invention is punchable upto 10 mm thickness. It can be fabricated easily. The weldability is also good. Table 2 hereunder reveals the plant performance test of the low alloy screen in a sintering plant. TABLE - II PERFORMANCE OF COLD SINTER SCREEN IN SP-II OF BSP SL. NO. SPECIFICATIONS STAINLESS STEEL SCREEN LOW ALLOY STEEL SCREEN 1 # Tonnage of sinter screened before rupture 4.6 lakhs tonnes 7.98 Lakhs tonnes 2 # Thickness of Bottom plates 6 mm 5 mm 3 # Hardness (BHN) 140 380 , Reference is invited to figure 6 which illustrates a cold sinter screen obtained of the low alloy steel obtained in accordance with the present invention. Importantly, the structure study of the steel obtained by the invention showed the presence of bainites. Increasing the hardness of the used components confirms the presence of retained austenite during oil quenching treatment. The process of the invention thus achieve to provide special end use characteristics to the steel. The steel produced by the process of the invention is also cost effective by way of the use of low content of chromium, nickel. Moreover the process advantageously provides adequate heat treatment schedule for improvement in hardness and thus increase in service life. 5 WE CLAIM 1 A process for manufacture of low alloy steel with improved wear resistant properties having chemical composition of C - 0 12 - 0.18% by wt., Mn = 0.8- 1.10% by wt., Si = 0.30 - 0.50% by wt., S = upto 0.020% by wt., P = upto 0 030% by wt., Cr = 0.50 - 0.90% by wt., Mo = 0.20 - 0.40% by wt., V = 0.02 - 0.06% by wt., Cu = 0.20 - 0.30% by wt., Ni = upto 0.12% by wt , A1 = 0.02 - 0.08% by wt and B = 0.003 - 0.006% by wt balance Fe comprising: providing the molten steel of said chemical composition ; tapping the molten steel in the temperature range of 1600 - 1660°C with or without addition of further metal/alloy; forming blooms from the molten metal ; soaking the blooms ; and obtaining the finished steel there from by conventional process steps preferably as plates in the minimum temperature of 800°C such as to thereby produce the required low alloy steel with high wear resistant properties. 2. A process as claimed in claim 1 wherein said step of forming blooms from said molten steel comprise : pouring molten steel from top to form ingots, soaking the ingots at 1280-1330°C for the period a 3-5 hrs followed by rolling. 3. A process as claimed in claim 1 wherein said step of forming the blooms from said molten steel comprise concasting the molten steel directly into blooms at turndish temperature of 1540-1560°C with high bending point temperature of at least 800°C. 4. A process as claimed in any one of claims 1- 3 wherein the plates are air cooled to ambient temperature. 6 5. A process as claimed in any one of claims 1-4 wherein the molten metal of desired chemical composition is prepared in BOF and/or EAF. 6. A process as claimed in anyone of claims 1-5 wherein molten metal of desired chemical composition is obtained from iron ore, spar, burnt dolo, sand mill scale steel, scarp and ferro alloys in required quantities 7. A process as claimed in any one of preceding claims wherein said step of tapping molten metal is carried out in a pre-heated ladle with addition of ferro alloys and aluminium. 8. A process as claimed in any one of preceding claims wherein the said step of soaking the bloom is carried out at a rate of 1 min. per mm thickness of blooms and plates preferably at a rate of 1 min. per mm thickness of blooms and plates. 9. A process as claimed in anyone of preceding claims, wherein the blooms are soaked and rolled in range of 900-950°C into plates 10.A process as claimed in anyone of preceding claims wherein said step of soaking the bloom is carried out in the temperature range of 1225 to 1260°C preferably for 1250°C a period of 3 to 5 hours preferably 4 hours and/or at the rate of 1 min per mm thickness of bloom. 11. A process for manufacturing a low alloy steel with improved wear resistant properties substantially as herein described and illustrated with reference to the accompanying figures and examples. Dated this 24th day of February 2000 7 A low alloy steel with improved wear resistant properties comprising chemical compositions of C = 0.12 - 0.18% by wt., Mn = 0.8 - 1.10% by wt.. Si = 0.30 -0.50% by wt., S = upto 0.020% by wt., P = upto 0.030% by wt., Cr = 0.50 - 0.90% by wt., Mo - 0.20 - 0.40% by wt., V = 0.02 - 0.06% by wt., Cu = 0.20 - 0.30% by wt., Ni = upto 0.12% by wt., Al = 0.02 - 0.08% by wt and B = 0.003 - 0.006% by wt. and a process for manufacturing the same. The low alloy steel with improved wear resistant properties is specifically useful as sinter screen in steel plant and also as wear resistant plates in ore and coal handling plants

Documents:

00111-cal-2000 abstract.pdf

00111-cal-2000 claims.pdf

00111-cal-2000 correspondence.pdf

00111-cal-2000 description(complete).pdf

00111-cal-2000 drawings.pdf

00111-cal-2000 form-1.pdf

00111-cal-2000 form-19.pdf

00111-cal-2000 form-2.pdf

00111-cal-2000 form-3.pdf

00111-cal-2000 pa.pdf

111-cal-2000-granted-abstract.pdf

111-cal-2000-granted-claims.pdf

111-cal-2000-granted-correspondence.pdf

111-cal-2000-granted-description (complete).pdf

111-cal-2000-granted-drawings.pdf

111-cal-2000-granted-examination report.pdf

111-cal-2000-granted-form 1.pdf

111-cal-2000-granted-form 19.pdf

111-cal-2000-granted-form 2.pdf

111-cal-2000-granted-form 3.pdf

111-cal-2000-granted-letter patent.pdf

111-cal-2000-granted-pa.pdf

111-cal-2000-granted-reply to examination report.pdf

111-cal-2000-granted-specification.pdf