JP2535899B2 - Structural steel - Google Patents

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a structural steel used for parts of automobiles and industrial machines.

[Prior art]

When manufacturing various parts from structural steel, it is inevitable that decarburization will occur from the surface in the process of hot working the material in the air or performing heat treatment such as annealing, normalizing, quenching-tempering . This decarburized layer does not harden even if it is hardened, and it causes unevenness of baking in the product, and lowers mechanical properties such as wear resistance and fatigue strength. Decarburization that occurs during heat treatment, as is well known,
Since oxygen in the atmosphere is induced, it can be prevented by using a furnace operating in a reducing or inert atmosphere or a vacuum furnace. However, these furnaces have high equipment costs and operating costs, and are not suitable for processing general-purpose structural steel. Decarburization during hot working is similar, but there is currently no means to prevent it. Therefore, it is the current situation that the decarburized layer produced is removed by machining or the like to obtain the final product.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a structural steel that exhibits anti-carburization resistance against hot working or heat treatment even in an atmosphere containing oxygen such as air.

[Means for Solving the Problems]

Structural steel showing anti-carburization resistance to heat treatment and working in an oxygen-containing atmosphere of the present invention, C: more than 0.30% 0.55% or less, Si: 0.1 ~ 0.5% and Mn: 0.3 ~ 2.0% in addition to It has an alloy composition containing 0.3% or less of one or two selected from Pb and Bi, and the balance being substantially Fe. In addition to the above basic composition, Cr: 5.0% or less, Ni:
1 or 2 selected from 4.0% or less and Mo: 1.0% or less
One or more kinds of steel may be contained, and a steel having such an alloy composition is also included in the structural steel of the present invention.

[Work]

The function of the alloy composition of the structural steel of the present invention and the reason for limiting the composition range will be described below. C: Exceeds 0.30% and 0.55% or less Gives strength to steel. If the content does not exceed the lower limit of 0.30%, the required strength cannot be obtained, and if the content exceeds the upper limit of 0.55%, the effect does not increase, and the ductility of the steel decreases, which is a disadvantage. Si: 0.1-0.5% Used as a deoxidizer. If the amount is less than 0.1%, there is no effect, and at 0.5%, the effect is saturated. Mn: 0.1-2.0% Added to improve the hardenability of steel, the lower limit of 0.
Even if the amount is less than 1%, the effect cannot be obtained. If added in a large amount, the machinability will decrease, so stop the amount so that it does not exceed 2.0%. Pb, Bi: 0.3% or less These elements have an action of suppressing decarburization of steel. If the total content exceeds 0.3%, hot workability is impaired. Ni: 4.0% or less, Cr: 5.0% or less, Mo: 1.0% or less These have the effects of enhancing the hardenability and improving the toughness and ductility of the steel, so it is advisable to add an appropriate amount if desired. The effects saturate near their respective upper limits.

【Example】

Steel with the alloy composition shown in the table was melted. N marked with *
No. 11 to No. 15 are comparative examples, and no mark is an example. The ingot was slab-rolled into a prism having a cross section of 115 mm on each side. It is heated to 1100 ° C in a heating furnace and hot rolled into a steel bar with a diameter of 35 mm.
It was left to cool to room temperature in the air on the cooling floor. A sample was taken from this steel bar and the depth of the decarburized layer was measured by microscopic observation. Furthermore, the outer surface of this steel bar was removed by lathing to a diameter of 33 mm, heated at 900 ° C for 1.5 hours in the air atmosphere and allowed to cool in the air. Also for this heat-treated steel bar, the depth of the decarburized layer was observed with a microscope. The results are shown in the table. As is clear from the data in the table, the comparative steels No. 11 to No. 15 are 0.03 to 0.07 mm in hot working, and
Whereas a decarburized layer with a thickness of 0.12 to 0.20 mm is produced, N
The structural steels of o.1 to No. 10 of the present invention had no decarburized layer, and it was considered from the observation of the structure that they were rather carburized.

【The invention's effect】

The structural steel of the present invention is substantially free from a decarburized layer even when subjected to hot working and heat treatment in an atmosphere where oxygen is present such as in the air. Therefore, it is not necessary to take measures such as adjusting the atmosphere of the furnace and removing the generated decarburized layer by machining. This leads to reduction of equipment cost and operation cost, omission of processes and improvement of material yield, and contributes to cost reduction of structural steel.

Claims (2)

(57) [Claims] 1. C: more than 0.30%, 0.55% or less, Si: 0.1-0.5%
And Mn: 0.3-2.0% plus 1 selected from Pb and Bi
A structural steel that contains 0.3% or less of one or two kinds, and the balance is substantially Fe, and exhibits decarburization resistance against heat treatment and processing in an oxygen-containing atmosphere. 2. C: more than 0.30%, 0.55% or less, Si: 0.1-0.5%
And Mn: 0.3-2.0% plus 1 selected from Pb and Bi
Alloy containing 0.3% or less of one kind or two kinds, further containing one or more kinds selected from Cr: 5.0% or less, Ni: 4.0% or less and Mo: 1.0% or less, and the balance being substantially Fe. Structural steel having a composition and exhibiting decarburization resistance against heat treatment and processing in an oxygen-containing atmosphere.