RU2250929C2 - Tool steel for forming rolls - Google Patents

Abstract

FIELD: metallurgy, in particular heat resistant steel composition for forming rolls in metal hot-rolling mill.

SUBSTANCE: claimed steel contains (mass %): carbon 0.21-0.40; silicium 0.60-1.50; manganese 0.20-0.60; chromium 4.00-6.00; nickel 0.20-2.00; vanadium 0.30-0.60; titanium 0.01-0.50; tellurium 0.001-0.020; aluminum 0.01-0.50; molybdenum or molybdenum and tungsten in total 1.00-2.00; and balance: iron. Molybdenum content in steel is not less than 0.40 mass %, and one mass part of molybdenum is equivalent to two mass parts of tungsten. Steel may additionally contain (mass %) calcium up to 0.30; zirconium up to 0.35; cerium up to 0.35, and boron up to 0.015. Content of inevitable impurities in claimed steel is limited: e.g. (mass %) sulfur, phosphorous and copper each not more than 0.040; lead, arsenic, and antimony each not more than 0.010.

EFFECT: decreased crack and erosion net forming on roll surface.

3 cl

Description

The invention relates to the field of ferrous metallurgy, in particular to the selection of the chemical composition of heat-resistant steel for rolling rolls of mills of hot deformation of metals.

Known steel grade 45XHM of the following chemical composition (wt.%): Carbon 0,40-0,50; silicon 0.17-0.37; manganese 0.50-0.80; chrome 1.30-1.70; nickel 1.20-1.60; molybdenum 0.10-0.30; sulfur and phosphorus no more than 0,040 (Marochnik of steels and alloys / Under the editorship of VG Sorokin. - M .: Mashinostroenie, 1989, pp. 438-440).

Steel 45KHNM is used for the manufacture of rolling rolls used for hot rolling of metals. This steel has heat resistance up to 600-650 ° C, but at the same time provides a hardness of not more than 341НВ. The disadvantage of this steel is the increased wear of the rolls due to low hardness.

Known for other steel grade 4X5MFS (adopted as a prototype), having the following chemical composition (wt.%): Carbon 0.32-0.40; silicon 0.90-1.20; manganese 0.20-0.50; chrome 4.50-5.50; vanadium 0.30-0.50; molybdenum 1.20-1.50; nickel not more than 0.35; copper no more than 0.30; sulfur and phosphorus no more than 0,030 (see ibid., pp. 405-406). This steel has high heat resistance (590 ° C) and at the same time has a significantly higher hardness of 47 HRC. The purpose of steel 4X5MFS is for the manufacture of hot deformation dies and die casting molds. However, in practice, it is also used for rolls of hot rolling of metals.

The disadvantage of steel 4X5MFS is the formation of cracks and a grid of heat on the working surface of the rolls, which leads to their failure. Cracks form under the influence of high alternating cyclic loads under the rotation conditions experienced by the rolls during operation. The heat grid is formed due to the thermal effect of the deformable metal.

The aim of the invention is to reduce the tendency of steel to crack and mesh high.

This goal is achieved by the fact that nickel, titanium, tellurium and aluminum are additionally introduced into the steel, and the components are selected in the following ratio (wt.%): Carbon 0.21-0.40; silicon 0.60-1.50; manganese 0.20-0.60; chrome 4.00-6.00; nickel 0.20-2.00; molybdenum or molybdenum and tungsten in the amount of 1.00-2.00; vanadium 0.30-0.60; titanium 0.01-0.50; tellurium 0.001-0.020; aluminum 0.01-0.50; iron is the rest, while the molybdenum content in the steel is at least 0.40 wt.%, and one mass fraction of molybdenum is equivalent to two mass fractions of tungsten.

In addition, steel may contain residual elements: sulfur, phosphorus and copper, not more than 0.040% each; lead, arsenic and antimony are not more than 0.10% of each. As a technological additive in the smelting of the proposed steel in molten metal can sit down (wt.%): Calcium up to 0.30; zirconium and cerium up to 0.35; boron up to 0.015.

In the proposed steel, the carbon content is set equal to 0.21-0.40%. When the carbon content is closer to the lower limit - 0.21-0.30%, the steel has a lower crack sensitivity, which allows it to be used for the manufacture of rolls experiencing large (ultimate) loads. The carbon content closer to the upper limit of 0.31-0.40% provides increased hardenability and allows the use of steel for rolls of large diameter and for rolls with a large depth of regrind calibers, but experiencing small and medium loads.

The proposed steel additionally contains nickel in an amount of 0.20-2.00%. At a carbon content of 0.21-0.30%, approximately 0.60-2.00% nickel is introduced to provide the required hardenability. In this case, steel can be used for rolls of large diameter and rolls with a large depth of regrinding calibers. If steel is used with a carbon content of 0.31-0.40%, the nickel content is sufficient in an amount of about 0.20-0.59%.

In order to increase hardenability at a carbon content closer to the lower limit, the upper silicon content is increased to 1.50%. When the carbon content is close to the upper limit, to avoid embrittlement of steel, the silicon content is reduced to 0.60%. Based on this, in the proposed steel, the silicon content is set in the range of 0.60-1.50%.

Slightly soluble titanium carbides, with its content of 0.01% or more, significantly grind the grain. In addition, with an increase in the titanium content to 0.10% or more, titanium carbides increase the wear resistance of steel. However, due to the fact that the formation of titanium carbides reduces the amount of free carbon, with a titanium content of more than 0.50%, a significant decrease in the hardenability of steel occurs. Based on this, titanium is introduced into the proposed steel in the range of 0.01-0.50%.

The residual sulfur in the deformed steel is partly in the form of strongly elongated sulfides of manganese and iron, and partly in the form of thin captures of these compounds along the grain boundaries. When heated, sulfur is oxidized to the SO ₃ compound, which causes intergranular corrosion and enhances the formation of a heat grid on the working surface of the rolls. Tellurium and sulfur in steel form an unlimited solution of manganese and iron sulfoselenides, which coagulate into granules and thereby clean the grain boundaries of sulfur. Due to this, the resulting compound SO _{3 is} in contact with a smaller number of boundaries, which dramatically reduces intergranular corrosion and the formation of a high-pressure network. Optimally, this process occurs when the ratio of selenium to sulfur is approximately 1: (3-10). Based on this and based on the actual sulfur content in the steel from about 0.010% to 0.040%, the tellurium content limits in the proposed steel are selected to be 0.001-0.020%.

A certain part of the aluminum introduced into the steel is located at the grain boundaries. Since aluminum has a much greater affinity for oxygen than sulfur, it prevents the formation of the SO ₃ compound. It also helps to reduce the height of the grid. With a higher sulfur content, more aluminum is required and vice versa. A reliable effect of aluminum on reducing the height of the grid is achieved when its content is in the range of 0.01-0.50% and is determined by the actual content of residual sulfur in the range of 0.010-0.040%.

In the proposed steel for rolls experiencing especially large specific loads, wear and heat, the molybdenum is increased to 2.00%, while molybdenum in excess of 0.40% can be replaced by tungsten based on the calculation: one mass fraction of molybdenum is equivalent to two mass fractions tungsten. The ratio of molybdenum to tungsten as 1: 2 is due to approximately the same ratio of their atomic weights (95.94: 183.85). To ensure resistance against tempering, molybdenum up to 0.40% is not replaced with tungsten.

Thus, the selected composition of the proposed steel allows us to solve the problem: to reduce the formation of cracks and heat grid on the rolling rolls in a wide range of modes of operation.

The brand name of the proposed steel 25X5NMFS.

Currently, preparations are underway for the production of rolls of steel for rolling steel pipes from the proposed steel. The roll parameters are as follows: barrel diameter - 935 mm, barrel height 590 mm, roll weight - 3100 kg, roll load - up to 1000 tons, caliber radius - 220 mm, number of caliber regrind - up to 10 (almost the entire depth of the barrel), temperature rolled metal 1000-1150 ° C.

Based on these parameters, the following chemical composition of steel for the manufacture of rolls (wt.%) Was selected: carbon 0.23-0.31; silicon 0.90-1.50; manganese 0.20-0.60; chromium 4.70-5.50; nickel 0.40-1.00; molybdenum 1.00-2.00; vanadium 0.30-0.60; titanium 0.02-0.08; tellurium 0.002-0.006; aluminum 0.01-0.05; sulfur, phosphorus, copper - up to 0.040. The steel provides for the replacement of 0.50-0.80% molybdenum with 1.00-1.60% tungsten.

Steel is smelted in the main arc furnace with a capacity of 20 tons. The mass of cast ingots is 10 tons. Forging mode - double draft and double hood, the degree of bite - at least 2.5. Heat treatment - hardening and double tempering for hardness 42-47 HRC.

Claims (3)

1. Tool heat-resistant steel for rolling rolls containing carbon, silicon, manganese, chromium, molybdenum, vanadium and iron, characterized in that it additionally contains Nickel, titanium, tellurium, aluminum, and molybdenum or molybdenum and tungsten in total in the following ratio elements, wt. %: Carbon 0.21-0.40 Silicon 0.60-1.50 Manganese 0.20-0.60 Chrome 4.00-6.00 Nickel 0.20-2.00 Vanadium 0.30-0.60 Titanium 0.01-0.50 Tellurium 0.001-0.020 Aluminum 0.01-0.50 Molybdenum or molybdenum and tungsten in the amount of 1.00-2.00 Iron Else the molybdenum content in the steel is at least 0.40 wt.%, and one mass fraction of molybdenum is equivalent to two mass fractions of tungsten. 2. Steel under item 1, characterized in that it further comprises, wt.%: Calcium Up to 0.30 Zirconium Up to 0.35 Cerium Up to 0.35 Bor To 0.015 3. Steel according to any one of p. 1 or 2, characterized in that it further comprises, wt.%: Sulfur, phosphorus and copper Not more than 0,040 each Lead, arsenic and antimony Not more than 0.10 each