Production method of high-carbon martensitic gas valve steel 85Cr18Mo2V silver bright bar material

Abstract

The invention provides a production method of a high-carbon martensitic gas valve steel 85Cr18Mo2V silver bright bar material, wherein the production method includes the following steps: adding steelscrap, high-carbon ferrochromium and other alloying materials in an electric-arc furnace, and carrying out alloy melting initial smelting; smelting with a steel ladle refining furnace; carrying out vacuum refining with a VD furnace; carrying out continuous casting with an arc square billet continuous casting machine; carrying out electroslag remelting; carrying out high speed wire rolling; annealing; straightening, polishing, inspecting and putting in storage. The production method of the gas valve steel 85Cr18Mo2V silver bright bar material adopts the metallurgical technology means of mothermaterial continuous casting and electroslag remelting to produce a steel billet, overcomes the problem of difficult continuous casting due to large high temperature deformation resistance of 85Cr18Mo2V, improves the morphology and distribution conditions of primary carbide, reduces various metallurgical defects, such as segregation and loosening, in the billet, effectively refines the structure ofthe original billet, greatly saves energy consumption and reduces the production cost; the production efficiency is greatly improved by using electroslag steel ingot one-heating forming; and steel wire rods are processed by grinding, pollution of pickling solutions and other problems are not generated, and the purposes of reducing the cost and increasing the efficiency are achieved.

Description

technical field [0001] The invention relates to a high-carbon martensitic gas valve steel and a manufacturing method thereof, in particular to a production method of a high-carbon martensitic gas valve steel 85Cr18Mo2V silver bright bar. Background technique [0002] Valve steel 85Cr18Mo2V is one of the martensitic valve steels in the national standard GB / T12773-2008 internal combustion engine valve steel and alloy bars. It contains the following components in weight percentage: C: 0.80~0.90%; Si: ≤1.00%; Mn: ≤1.50%; P: ≤0.040%; S≤0.030%; Cr: 16.50~18.50%; Mo: 2.00~2.50%; V: 0.30~0.60%; For Fe and inevitable impurity elements. It is mainly used in the manufacture of intake valves for heavy-duty or high-load diesel locomotives. The high-carbon martensitic valve steel 85Cr18Mo2V is developed on the basis of 80Cr20Si2Ni (US steel type XB, Japanese steel type SUH4). 80Cr20Si2Ni was developed and applied in European and American countries in the mid-1950s. The purpose was to im...

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Problems solved by technology

[0003] High-carbon martensitic valve steel 85Cr18Mo2V is generally delivered in the state of bright silver bars after annealing. The bars with a specification of φ5-15mm are easy to appear in the annealed structure due to their high carbon and chromium content. There are many carbides. The high-carbon martensitic steel produced by the method of conventional electric furnace plus refining outside the furnace, due to the selection of crystallization during pouring, the primary carbides are too large, and the grade of banded carbides after rolling is higher. , the carbides are unevenly distributed, and sometimes contain twin carbides. These uneven carbides not only reduce the plasticity of the steel, but also affect the high-temperature fatigue performance indicators of the product.

In addition, during the straightening process of hot-rolled wire rod, due to the high hardness and strong brittleness of the material, fractures often occur in the process of uncoiling and straightening. more difficult

[0004] In the existing patent technology and literature, there are many descriptions on the improvement methods of high-carbon martensitic steel carbides. For example, the patent ZL201410348136.1 points out that the adjustment of components and the control of heat treatment process can improve the morphology and distribution characteristics of carbides. However, this method is only for 9Cr18 stainless steel forging products, and the feasibility of this method for high-speed wire products with a larger compression ratio remains to be verified.

In the patent 201010153186.6, a production method of martensitic gas valve steel bar is pointed out, which does not involve the production and manufacturing process of the wire rod, mainly through drawing and straightening the wire rod, and then polishing to obtain a polished horse. Martensitic gas valve steel wire rod, this method uses processes such as alkali washing and sulfuric acid pickling, mixed pickling, epidermal film agent and lubricant in the drawing process to carry out surface treatment on the martensitic valve steel wire rod, although it can Qualified rods are obtained, but chemical raw materials such as alkali washing, pickling, coating agents, lubricants, etc. will produce more chromium-containing pollutant emissions. In today's increasingly stringent environmental protection requirements, this process is very undesirable, and in the process The light drawing and two-roll straightening will aggravate the work hardening phenomenon of 85Cr18Mo2V wire rod, making the material more "brittle" and easy to "break", affecting the yield

In Example 1 of this patent, it is explained that the preparation process of 85Cr18Mo2V billet is: electric arc + ladle refining → forging billet opening → forging billet annealing → disc rolling → disc annealing treatment, as can be seen from the process flow, forging Billet opening and coil rolling require the process of "two fires to form a material", and include annealing of forging billets, multiple heating of billets and forging billets will seriously restrict the production efficiency and cost of 85Cr18Mo2V wire rod

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