In this catalogue, the mechanical values are given for castings with common thickness of about 40 mm.
Generally, these values will somewhat increase with a decrease of the thickness. When increasing the thickness, the mechanical values will decline proportionally. In hardened and tempered steels the increase or decrease of the values will be slightly more significant depending on the hardenability of the particular steel and iron alloy grades under various tempering temperature.
Designation of the mechanical properties
In the catalogue are used signs, units and definitions, used throughout the world according to the valid norms EN and SI valid for metallic materials as approved and published by the European Normalization Organization CEN/CENELEC, Brussels, Belgium. Member states are obliged to confer to these EN (Euronorms) the national statute without any changes gradually as they will be issued.
The results of the tensile tests given here have been attained on the short specimen, normalized according to the ratio rule expressed by theorem:
L0 = k x √ S0
where L0 is the initial measured length in mm, k is the internationally accepted constant 5.65 (= L0/ √ S0), S0 is the average surface area of the round bar in mm2
L0 = 5 d
where d is the diameter of the bar in mm
Without such specified dimensional parameters of the specimens and their mentioning in the accompanying certificate, the information derived from the values is insufficient for comparison purposes and worthless to designer. The values of the tensile tests cannot be substituted and are reliable for a resistance to tensile stress up to 1000 N/mm2. At higher strengths, deviations begin to appear growing proportionally with growing strength. They origin lies in constantly more difficult methods of measuring.
Notch toughness tests
OMore commonly in the world is used a V-shaped notch with a depth 2 mm in the specimen, where slightly higher values have been found than at a U-shaped notch. More often is preferred requirement on V-shaped notch that it is more similar to the notches on component parts after tools as remains of cutting operation. Any scratch on components is taked for a nucleus of fatique fracture.
cutting operation. Any scratch on components is taked for a nucleus of fatique fracture. In the catalogue the notch toughness is given for the U-form (KCU 3) and is expressed in J/cm2 units. The values with the V-notch are more decisive, however they have not been verified in the given materials. They are also given under the definition “Impact energy” indicated by K and expressed in J unit subtracted directly on the scale of CHARPY-hammers.
The notch toughness KC is a quotient of the impact energy and cross section of the testing bar in the place of notch:
KC = K/S0
where K is the value of the impact energy in J, S0 is the cross section area under the notch in cm2.
The value of the impact energy can be derived as follows:
K = KC x S0
There is no method for converting the results of these values, in determining the notch impact toughness or impact energy, ascertained on the specimen of one type, onto values of other types of specimens. The bars with cross section 10 x 10 mm are used for testing castings (MESNAGER).
Testing of properties and values of unmachinable materials
ZThe preparing of samples for tensile strength and impact test (notch toughness) is very difficult and expensive in these cases. Especially at abrasion-resistant materials, where also high hardness is required, the usual classical tests are not made. Their results do not give reliable mechanical values, especially the A, Z and Re values give slight differences that are difficult to measure.
They are replaced by samples of alloyed and unmachined bars with Ø 30 mm and length L0 ≥ 350 mm. The sample is placed on two supports with rounded edges, the axial distance between the supports being constant L0 = 300 mm (the length to be tested). In the middle of the example L0/2 a force F acts on the bar over the rounded plug until it breaks. At the moment of the fracture is measured:
- the deflection of the bar in mm
- the force F required for breaking in N
- fracture surface can also be evaluated, where the relation of the ductile fracture to the brittle fracture, transcrystalline fracture to the intercrystalline fracture, grain size and macro-purity are determined.
The test thus performed provides more reliable information than the tensile and impact tests. Another permitted way of attaining classical bars for performing tensile and notch impact test is to cast the bars directly into sand moulds usually made by HB (HOT-BOX) method. These bars are smooth and have quite precise form and are not machined any more.
The values attained from such cast bars cannot be considered as representative, but rather informative, because their crystallization is slightly different from that of castings with another thickness.
Classification of weldability
The material can be welded reliably at room temperatures and it is suitable even for dynamically stressed joints up to 25 mm thick. Over 25 mm the welding is possible under specific conditions. The producer guarantees weldability.
Guaranteed, under specific conditions
The material is weldable only under conditions as specified for each individual steel. The producer guarantees weldability only when the specified conditions have been fulfilled. Dynamic stress is still permissible.
The producer does not guarantee weldability, however in most cases the welded joints are still suitable when specified conditions have been maintained. Dynamic stress is limited.
A suitable quality of welded joints cannot be achieved even if special measures have been kept. Weld quality can be slightly improved when special welding methods are used that are not given in the cataloque. Such types of steels and alloys are not recommended for welding or the welding up, welding and patching their surface with hardmetal against abrasion is even forbidden.
Such materials are usually not suitable for welding.
Classification of machinability when using sintered carbide by cutting tools
The hardness and strength of the part to be machined is not always deciding for its machinability. However a constant border between machinability and unmachinability cannot be generally specified according to the above mentioned properties. Therefore the machinability should be given separately according to following classification for every material grade.
Without any difficulties, including tools made from tool steels (thread cutting into holes).
Without any problems at various cutting speed. Cutting threads into holes by taps of tool steel is possible.
At higher toughness of the material to be machined, when cutting is interrupted and the cutting speed is substantially lower. The thread cutting with tool steel taps is possible only exceptionally and only at some steel grades after their soft annealing.
he angles of cutting tool blades should be modified and the cutting speed very low. When the cuttings are interrupted, the material cannot be machined.
In exceptional cases the cutting tool is capable of chip reduction, but its cutting edge is blunted so quickly that it is not possible to achieve continuous machined area and its flatness. On the basis of this fact the material is considered unmachinable by cutting operation.
Conversion table of final condition of ferroalloys after heat treatments
|Symbol according to ČSN EN 10027-1||First additional number||Final condition of ferroalloys to castings in dependence on heat treatmens|
|+SR||.2||annealed (with the indicated method of annealing)|
|+AT||.4||after solution annealing (only by the austenitic steels)|
|+NT||.5||normalized and tempered|
|+QT||.6||hardening treated to lower strength,usual by the appropriate steel|
|+QT||.7||hardening treated to median strength,usual by the appropriate steel|
|+QT||.8||hardening treated to upper strength,usual by the appropriate steel|
|+QT||.9||conditions after heat treatment, these cannot be inscribe with No.1 – .8|