RU2219277C1 - High-strength steel - Google Patents

Abstract

FIELD: ferrous metallurgy. SUBSTANCE: invention relates to steels used as long-measured tool used in hot rolling. Invention proposes steel comprising the following components, wt. -%: carbon, 0.32-0.36; manganese, 0.30-0.50; silicon, 0.90-1.10; chrome, 5.15-5.50; molybdenum, 1.20-1.35; vanadium, 0.90-1.10; nitrogen, 0.005-0.015; niobium, 0.0005-0.05; calcium, 0.005-0.025; zirconium, 0.005-0.025; aluminum, 0.01-0.035; iron, the balance. EFFECT: enhanced hardness and hardenability in air of steel. 2 tbl

Description

 The invention relates to the field of ferrous metallurgy, in particular to steels used in metallurgy for long tools with a diameter of 220-450 mm used in hot rolling of pipes.

Known steel grade 4X3VMF of the following composition wt.%:
Carbon - 0.40-0.48
Silicon - 0.60-0.90
Manganese - 0.30-0.60
Sulfur - Not more than 0,030
Phosphorus - Not more than 0,030
Chrome - 2.80-3.50
Nickel - No more than 0.35
Molybdenum - 0.40-0.60
Vanadium - 0.60-0.90
Tungsten - 0.60 -1.00
Closest to the proposed steel is steel grade 4X5MF1S GOST 5950-73 of the following composition, wt.%:
Carbon - 0.37-0.44
Silicon - 0.9-1.2
Manganese - 0.2-0.5
Chrome - 4.5-5.5
Vanadium - 0.8-1.1
Molybdenum - 1.2-1.5
Nickel - No more than 0.35
Copper - Not more than 0.30
Sulfur - Not more than 0,030
Phosphorus - Not more than 0,030
This steel is intended for the manufacture of tools with cross sections up to 400 mm. The specified level of mechanical properties is also provided by quenching in oil with subsequent tempering. However, for this steel grade, when replacing “quenching in oil” with “quenching in air”, hardenability decreases. In addition, the increased carbon content leads to a sharp decrease in the temperature of the beginning and end of the martensitic transformation, as a result of which up to 40% of residual austenite remains in the metal, which also affects the level of mechanical properties during operation. Thus, the main disadvantage of the known steel is the low hardenability during cooling in air.

 The objective of the invention is to increase hardenability during cooling in air.

To achieve this goal, nitrogen, niobium, calcium, zirconium and aluminum are additionally introduced into steel containing carbon, manganese, silicon, chromium, molybdenum, vanadium, in the following ratio:
Carbon - 0.32-0.36
Manganese - 0.30-0.50
Silicon - 0.90-1.10
Chrome - 5.15-5.50
Molybdenum - 1.20-1.35
Vanadium - 0.90-1.10
Nitrogen - 0.005-0.015
Niobium - 0.0005-0.05
Calcium - 0.05-0.025
Zirconium - 0.005-0.025
Aluminum - 0.01-0.035
Iron - Else
The choice of elements for alloying the selected steel grade was determined by the required properties and cost.

 Carbon in steel in an amount of C = 0.32-0.36% is selected in order to ensure high ductility and reduce brittleness.

 The manganese content in the amount of Mn = 0.3-0.5% is selected from the condition of ensuring full deoxidation of the steel, increasing hardenability and lowering the temperature of the cold brittleness threshold.

 Chrome in steel in an amount of Cr = 5.15-5.50% increases deoxidation.

 Silicon in the amount of Si = 0.9-1.10% is an active deoxidizer of steel and reduces the sensitivity to overheating.

 The molybdenum content in steel Mo = 1.20-1.35% provides an increase in toughness and reduces sensitivity to temper brittleness.

 The content of vanadium in an amount of V = 0.9-1.10% contributes to the grinding of grain.

 Boron in steel in an amount of B = 0.0005-0.005% reduces the tendency to grain growth.

 Aluminum in an amount of Al = 0.010-0.035% provides complete deoxidation of the steel and contributes to the obtaining of fine-grained structure.

 The calcium content in the amount of Ca = 0.005-0.010% is selected from the condition of ensuring complete deoxidation of the steel and contributes to the production of small globular non-metallic inclusions.

 The cerium content in the amount of Ce = 0.005-0.025% ensures complete deoxidation of the steel and contributes to the production of small globular inclusions.

 Known and proposed steel was smelted in an induction furnace IST-16 using the following charge materials: 70 LF, FS-45 ferrosilicon, FMP-1 ferromanganese GOST 4755-80, GOST 475779 ferrochrome, GOST 4579-70 ferromolybdenum, TU 145-98 ferrovanadium -78, ferro-tungsten GOST 17293-82, nickel H-1, niobium FB-10, silicocalcium SK-10 GOST 47622-71, ferrosilicon zirconium FSTsR-25 TU 145-83-77 alloy KhAK-1.

 The chemical composition of the heats is given in table. 1.

These experimental ingots were forged on a bar measuring 50x500 mm. After forging the forgings underwent preliminary heat treatment - annealing at a temperature of 680 ^o C.

 Known and claimed steel were compared at a critical quenching rate, providing 50% martensite and 50% bainite (V cr. 50). The amount of residual austenite was determined by the metallographic method (Au ost).

 The temperature of the beginning and end of the transformation was determined by dilatometric method.

 The test results are given in table. 2.

 From the above studies it is seen that the proposed steel is characterized by increased hardenability and hardness.

Claims (1)

Steel containing carbon, manganese, silicon, chromium, molybdenum, vanadium and iron, characterized in that it additionally contains nitrogen, niobium, calcium, zirconium and aluminum in the following components, wt.%: Carbon 0.32 - 0.36 Manganese 0.30 - 0.50 Silicon 0.90 - 1.10 Chrome 5.15 - 5.50 Molybdenum 1.20 - 1.35 Vanadium 0.90 - 1.10 Nitrogen 0.005 - 0.015 Niobium 0.0005 - 0.05 Calcium 0.005 - 0.025 Zirconium 0.005 - 0.025 Aluminum 0.01 - 0.035 Iron Else

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